Sound motion picture apparatus



June 10, 1941. 4 wlTTEL 2,245,240

souuumontm PICTURE APPARATUS Filed May 19, 1939 2a J 27 2e Patented June 10, 1941 SGUND MOTION PICTURE APPARATUS tto Wittel, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application Ma 19, 1939, Serial No. 274,656

4 Claims.

This invention relates to sound motion picture apparatus either projectors or cameras and particularly to the latter. It relates specifically to the film driving mechanisms in such apparatus.

It isan object of the invention to provide means for advancing the film with a uniform motion through the point at which the sound track is scanned. Obviously unless the film is constrained to move at a uniform and constant rate, there will be a distortion in the sound being recorded or reproduced.

It is a particular object of the invention to provide means for minimizing or eliminating entirely any non-uniformity of film motion due-to a lateral motion, end-play or wobble of any of the gears in the train which drives the film.

It is well known that one of the smoothest types of gears comprises a disc gear driven by a worm. She term disc gear is here used to include both worm gear and spur gear. Such arrangements have the worm rotating at right angles to the disc gear and employ as a disc gear, a worm gear with oblique teeth set at an angle to match the pitch of the worm. However such systems are not quite perfect and any end-play, lateral motion or wobble'of the disc gear (specifically a worm gear) causes these oblique teeth to shift so that the lateral motion is partially converted into tangential motion which, of course, involves a change in rotational speed of the disc gear. It is the specific purpose of the present invention to minimize or eliminate entirely any change in rotational speed due to such end-play or wobble of the disc gear.

According to the invention, the drum or sprocket which carries the film through the sound gate is driven, either directly or through a series of driving members by a disc gear which in turn is driven by a worm rotating at an acute angle (less than 90) to the disc gear. Preferably the disc gear is a spur gear and has straight teeth (i. e. teeth parallel to the axis of rotation of this disc) and the worm is set so that its teeth (threads) mesh properly with the straight teeth. That is, the worm is set to rotate at an acute angle to the disc gear Which angle is equal to the pitch of the worm. This defines equal as it is used in this specification and the accompanying claims.

With the disc gear and worm set in this preferable relation to each other, the rotation of the disc gear (specifically a spur gear in this case) is independent of any lateral movement of this gear (provided of course that it doesnt slip entirely out of mesh). This is due to the fact that any such lateral motion such as due to end-play or wobble merely causes the disc teeth to move parallel to themselves along the worm teeth so that there is no tangential component of this lateral motion.

While the preferred embodiment thus described is necessary to eliminate completely the effects of end-play and wobble, there is a certain degree of improvement obtainable when the invention is only partially applied, i. e. when the worm is'set at an angle only approximating its pitch and the disc gear teeth are still slightly oblique. This less preferable embodiment may be necessary to allow a more compactor convenient arrangement of the gear train.

It is desirable that the invention be employed in that part of thefilm driving mechanism which controls the steadiness of the film passing through the sound gate, but it is not necessary that this be the sole force which advances the film. In those systems which employ a viscous drive whereby the sound head drum is maintained-at a speed slightly less than the film speed (e. g. 1 less) andin which the film itself (driven otherwise) assists in driving the sounddr-um, the

invention is applied to the drum driving system and/or the film driving system. I prefer, in a sound camera for example, to couple the sound head drum or sprocket to a fiy wheel, to drive the drum and flywheel by a viscous drive, to drive the viscous drive by a disc gear and to drive the disc gear by a worm mounted in accordance with the present invention. The worm may also drive the other moving parts of the camera (preferably through a mechanical filter to prevent any feed back of the intermittent motions) and thus may be coupled to a film driving sprocket which pulls the film from the-sound drum at a speed slightly greater'than that at which the viscous drive is rotating the drum. Thus the film assists in driving the drum and drives it at a speed slightly greater than that at which the viscous drive is moving.

Other objects and advantages of the present invention will be apparent from the following specification when read in connection with the accompanying drawing in which:

Fig. 1 is a perspective view of one embodiment of the invention.

Fig. 2 is a front elevation of the arrangement shown in Fig, 1.

Fig. 3 illustrates another embodiment of the invention.

Fig. 4 is an enlarged fragmentary view of a gear coupling according to the invention.

In Figs. 1 and 2, a sound film (a sensitive film when the invention is used in a camera, a film with pictures and a sound track when used in a projector) is advanced with a uniform motion by a sprocket I I. The sound track on the film I is scanned by means of an optical system including a light source I2 and lenses I3. The sound gate is indicated by the point Hand is known as a sound gate, whether or not there is any mechanical means for defining this particular point. The sprocket II is mounted on a shaft I4 and rotated thereby. The shaft I4 is in turn driven by a disc gear I having straight teeth parallel to the axis of rotation thereof, i. e. parallel to the shaft M. According to the invention,. this disc gear I5 (specifically a spur gear) is driven The crown gear 3| mounted on a shaft 32 drives a film sprocket 33 which advances the film III around the sound drum and pulls it from the sound drum at a speed slightly greater than that at which the viscous drive 23 rotates this drum 20. That is, the gear linkages between the worm 26 and the disc gear 24 provide slightly less peripheral speed than that ,provided by the beveled gear 30 and crown gear 3I. Thus the film I0 assists to a slight degree in driving the sound drum 2D. The drum is mainly driven by the viscous drive 23, since the ease with which the fiy wheel 22'maybe rotated with respect to the ioidrive thesound drum 20 at a speed slightly an acute angle to the disc gear I 5.

In the preferred embodiment illustrated, the I angle at which this worm is set is equal to the pitch thereof. This provides that the threads of the worm I 6 mesh'properly with the teeth of the spur gear I5 and at the point of mesh,the threads of the Worm IB 'are also parallel to the shaft I4. Any end-play of the disc I5 and shaft I4, any motion of the gear I5 on the shaft I4 or any wobble of the gear I5 about an axis at right angles to the shaft I4 will merely cause the teeth of the disc gear I5 to m'eshwith the worm I6 at a slightly different point, but this change will introduce no additional rotation of the-disc I5. Lamp I2 may be a'glow lamp or ordinary sound valves may be used for recording. I

In Figs. 1 and 2 the worm I6 is a triple thread gear.

The meshing of the gears'is best illustrated in Fig. 4 where a double thread worm I6 meshes exactly with a disc gear I5 whose teeth are parallel to its axis (l. e. a spur gear).

In the arrangement shown in Fig. 3, the invention is combined with a system'wherein the sound drum is driven by a viscous drive at a speed about 1% less than that at which this drum is driven by the film itself. In the arrangement shown, the sound gate is just to one side of the cylinder 20 (in this case a drumrather than a sprocket) which is mounted on a shaft '2I to rotate with a fiy wheel 22. This drum 20 and fly wheel 22 are driven by a viscousdrive comprising a housing 23 fittingclosely around the fly wheel 22 and separated therefrom by aviscous mediumsuch asoil in the chamber 28. The housing 23 is mounted on ball bearings 21 and is driven by a disc gear 24, all shown in cross section. I iI According to the invention this disc gear 24'is driven by a worm 26 mounted at an acute angle to the disc gear equal to the pitch of the worm. The worm 26 is carried by a shaft which also drives a crown gear 3I through a beveled gear 30.

ill

greater than that at which the housing 23 is rotatingfbut the viscous medium 28 prevents any great difference in speed between the drum 20 and the housing 23. Obviously, the shaft 2| must be free to rotate'in the bearings 34.

Having thus describedtwo preferred embodiments of my invention,I wish to point out that it is not'limited to the specific structures but is of the scope of theappended claims.

What I claim and desire to secure by Letters Patent of the United States is: 1

1. A device'for providing uniform film motion in sound motion picture apparatus comprising means in contact with the film for advancing it, means including a disc gear for driving the film advancing means and a worm in mesh with the disc gear for driving the'latter, said worm rotat ing in a plane at an acute'angle with the disc gear. I

2. A deviceaccording to claim l in which the disc gear has teeth parallel to the axis of rotation of the gear and said acute angle is equal to the pitch of the worm. I

3. In a sound motion picture camera, a device for advancingthe film-with a uniform motion past the sound gate, comprising a rotating cylinder adjacent to the'sound gate for guiding the film through thesound gate, a fiy wheel coupled to the cylinder to rotate therewith, viscous driving means for rotating the fiy wheel and cylinder, a disc gear with teethparallel to its axis of rotation for driving the viscous driving means, and a worm in mesh with the disc gear for driving the latter, said worm rotating at an angle to the disc gear equal to the pitch of said worm.

4. A device according to claim 3 in which there is a film sprocket also driven by the worm, said sprocket being positioned and geared to the wormto pull the film fr'om the rotating cylinder ata rate slightly faster than that at which the viscous driving means rotates said cylinder, whereby the" film itself assists in driving the cylinder. 1

' I OTTO WITTEL. 

